Analytical combustion train



Jan. 26, 1965 Filed Feb. 27, 1961 .1. J. J. STAUNTON ETAL 3,167,396

ANALYTICAL COMBUSTION TRAIN 2 Sheets-Sheet 2 ATTORNEYS.

United States Patent 3,167,396 ANALYTICAL CGMEUfiTlQN TRAEN John J. J. Staunton, Gals Park, Lewis Malter, Niles, William J. Gleason, Villa Park, and Rome W. Bull, Mount Prospect, Ill., assignors, by mesne assignments, to Coleman Instruments Corporation, Maywood, iii a corporation of Delaware Filed Feb. 27, 1961, Ser. No. 91,713 7 Qlaims. (til. 23-23%) --This invention relates to an improved construction for an analytical train used in chemical analytical procedures. Such procedures often involve the analysis of a material by heating it so as to pyrolyze it or break it down into its components. These components are then reacted with a stream of gas and the reaction products are absorbed into material which can be weighed, or the products may be analyzed by some other method such as titration, colorim'etry, or by volumetric methods. The combustion train is the device in which the initial pyrolysis or combustion is completed.

In the conventional combustion train the sample to be analyzed is disposed within a tube, as are the absorbing materials. These tubes are disposed in horizontal position. A horizontally disposed combustion or absorption tube must be very tightly packed so that the motion of the gas flowing through the tube will not jiggle the grains of packing material and cause them to settle to the bottom of the tube, leaving a clear. path or channel along the top side of the tube through which the gas flows. Under such conditions the tlowing gas will not contact uniformly the packing within the tube. Furthermore, when the packing is tight to minimize the channeling and settling the resistance of the tube to fluid flow is greatly increased because of the friction. Another disadvantage of the conventional horizontal combustion and absorption tubes lies in the fact that water deposits on the walls of the tube and settles to the bottom, where it is difficult to pick up by the flowing gas.

A primary object of the present invention is to eliminate the foregoing objections by providing a combustion train in which the combustion and absorption tubes are vertically disposed. We have found that such vertical tubes need not be tightly packed because no amount of agitation by the gas can cause channeling. The gas flows through the entire cross section of the tube in contact with substantially all of the particles comprising the packing. Such packings are referred to in the claims as solid particulate material. Consequently, the rate at which the gas flows through the train can be greatly increased to speed up the analysis and permit analysis of larger samples because more gas is available to carry out the combustion process in a given time. Moreover, the higher flow rate also causes the water vapor in the tube to become entrained more readily and carried farther down the train before condensation takes place. Thus the water absorbing material can be placed at a point well separated from the combustion tube. This gives the gas stream time to cool and the water absorber is not heated either by the gas stream or by the proximity of the furnaces used to heat the combustion tube.

Other advantages result from the use of a combustion train in which the tube members are vertically disposed: greater ease of operation, increased accuracy, prompt results, lower cost, a wider variety in the state and size of the sample, ready adaptability to many diitercnt analytical procedures, and a great saving in bench top space. Three or more complete instruments constructed in accordance with the present invention may be mounted in the same space used by only one of the prior conventional instruments.

3,167,396 Patented Jan. 26, 1965 Another object of the invention is to provide an improved means for mounting the absorption tubes between the conduits which connect them to adjoining tubes. This means provides for a fluid-tight seal between the tube and the conduit without using any waxes or lubricants and consequently nothing requires wiping before weighing.

Another object of the invention is to provide a vertically disposed analytical combustion train in which means is provided for feeding gas through the train at two different flow rates.

These and other objects and advantages of our inven-- tion will be apparent from the following description, when read in conjunction with the accompanying drawings, in which FIGURE 1 is a semi-diagrammatic illustration of an analytical combustion train constructed in accordance with the invention;

FIGURE 2 is a sectional view through an absorption tube showing the construction of the quick disconnect fittings between which the tube is disposed;

FIGURES 3 and 4 are sectional views through the end of an absorption tube, showing an alternative form of sealing means in open and closed positions respectively;

FIGURE 5 is a top view of the sealing means shown in FIGURE 3;

FIGURE 6 is a sectional view through an absorption tube which has been modified to include check valves so that the gas flow is in one direction only;

FlGURE 7 is another alternative construction for an absorption tube shown in section in which the open end carries a ground glass plug; and

FEGURE 8 is a sectional view of a modified construction for a quick disconnect fitting.

The analytical combustion train shown in FIGURE 1 is especially adapted for use as a hydrogen and carbon analyzer. It will be understood, however, that this invention is also suitable for use with nitrogen analyzers and for the analysis of other chemicals which utilizecombustion trains and absorption tubes in their analysis. By using different carrier gases and ditferent measurement sections such as titrators, colorimeters, conductivity cells, or other readout devices, and appropriately programming the system, such things as sulfur, halogens, phosphorus, oxygen and other sample constituents-can be determined. With all of these the novel advantages of our system will obtain in greater or lesser degree.

Referring specifically to FIGURE 1, an oxygen tank is identified by the numeral 1 and serves to provide oxygen for the analysis. In the conduit between the oxygen cylinder 1 and the absorption tube 5 we have provided a number of devices for measuring and regulating the flow of oxygen to the train. These include a regulator 2, a pressure indicating gauge 12, a flow meter 3, anda high flow regulating valve 4. For automatic operation a pair of solenoid valves are provided in series and are designated as 13 and 14. A low flow regulating valve 15 is provided in a bypass conduit. By manually adjusting the high flow regulating valve 4 the gas may flow at a rate ranging between and 200 cubic centimeters per minute. Gas flows at this rate to the absorber 5 when both solenoid valves 13 and 14 are open. A lower flow rate, say between 20 and 50 cc. per minute, may be obtained when the solenoid valve 14 is closed and the low flow regulating valve 15 is opened and manually adjusted to the desired flow rate within the aforesaid range. The solenoid valves 13 and 14 may be controlled by a timer on the instrument which is not shown. When both solenoid valves are closed, flow to the train is shut off completely. The pie-treat absorption tube 5 is packed in Lhe center with ascarite which is a commercial preparation consisting of sodium hydroxide on asbestos and is identified in the drawing by the numeral 18. The upper and lower thirds of the tube are filled with magnesium perchlorate coated vermiculite, identified by the numeral 19. The upper layer of perchlorate removes moisture from the oxygen, the middle layer removes carbon dioxide, and the lower layer removes any further moisture released during passage through the middle layer. a 1

The lower end of the tube 5 connects to the upper end of the combustion tube 6 which contains a platinum wire gauze choke 20 to stop back travel of reaction products during combustion. The sample to be analyzed is designated by the numeral 7 and is disposed downstream of the platinum wire choke. Two bodies of copper oxide granules 22, 24 are disposed between quartz wool plugs 21 and 25. Interposed between the two bodies of copper oxide granulesis a layer of platinized asbestos 23 which catalyzes the combustion reactions and breaks down hydrocarbon radicals such as methane. The first body of copper oxide granules disperses and heats the com- In the relatively long conduit betweenthe bottom of the combustion tube 6 and the top of the absorption tube 9 we have provided a vent valve 16 to permit purge oxygen at the beginning of a run to escape to the atmosphere carryingwith' it air and moisture. As gas passes through the long conduit it is cooled by transfer of heat to the air surrounding the conduit. Absorption tube 9 contains a packing of magnesium perchlorate in vermiculite to absorb water formedduringcombustion. The weight of this water is a measure of'the hydrogen content of the sample. The water absorption tube 9Tconnects' to a scrubber 10 containing manganese dioxide 27 for removing the. oxides of nitrogen and certain other unwanted of trouble in the prior art trains. ,It is therefore apparent that a fgghfir feature of our system is the increase in speed and uracy of the Water determination.

It must not be conjecturedthata simple increase in rate of flow of the gas, if this were possible in the prior art horizontal system, would 7 give the same results as those just explained. To simply increasethe flow rate of any given system would be impractical. During the first part of the combustion a slow flow rate is highly desir able because at this time a large evolution of volatiles is given off by the sample and time must be allowed in the combustion tube to break down and react these with the carrier gas. Also a high flow rate during this part of i the cycle would minimize deep penetration of the absorbing material by thegas. For example, if all of the oxides of nitrogen were not absorbed by the manganese dioxide I absorber 27 they would carry over into the CO absorber 11 and. give faulty results. In accordance with the present invention, we have incorporated the double flow will deposit on the top of the packing and then, Urged by .the gas stream, will flow down through the tube, becoming effectively and uniformly entrained in the interstices of the packing, This greatly increases the amount of water that can "be picked up as compared with a packing disposed in a horizontal tube. To further this 'elfcct even more, we have used carrier based anhydrous mag nesium perchlorate, where the carrier is a highly porous vermiculite, to increase the absorptive efficiency. This has the advantage that, whereas the granular magnesium perchlorate will puddle and become wet at the top of the tube if a large amount of water comes through and will then also'absonb" oxides of nitrogen causing error, the

combustion products. A packing of magnesium per-1 chlorate 28 removes any water given up by the manganese dioxide packing. f The tube 10 and the pretreat tube 5 function through a numberof analytical cycles before exhaustion of their contents necessitates replacement. An-

' other conduit connects the top of the scrubber 10 tov the top of the carbon dioxide absorption tube 11. Tube 11 is packed with ascarite 29 for absorbing the carbon dioxide inthe gas stream," and the moisture given off cross section of the tube so that uniform contact between the gases and the absorption media is obtained. 'In analyzing large samples whichraise the moisturev content of the gas stream the high flow rate. afiorded by the loose packing is particularly effective in keeping this moisture movingzthrough the train. It will be noted that the absorption tube'9 has been placed at a point well separatedfrom the combustion tube. This is possible because the moisture in the air is, carried 'by the swiftly moving gas stream into the absorber rather than being deposited within the conduit. Because the gas stream has time to cool the water absorber is not heated. and it may be removed promptly for weighing. There is no drift'of the'tubes weight due to cooling, nor is there any inaccuracy caused by suction of room air and moisture-into the tube as it cools. This isa common source carrier based perchlorate will not become wet but will spread its waterpickup throughout thelength of the tube, eliminating the above difiiculty. Asa result, we have ben able to reduce'the size of the absorber tubes while still maintaining capacity to handle large samples.

The reduction in the size of the absorber tube is in itself an important contribution to accuracy of measurement. We have been able,'through the means previously described, to keep the weight of tubes 9 and 11 with contents below 20 grams. This makes it possible. to weigh these tubes on a modern one-pan balance to a degree of accuracy which would be impractical with a heavier tube. In addition, considerable time is saved bythe use of such a balance.

from neoprene rubber, silicone rubber, or other. resilient.

material which is resistant to the gases and combustion products flowing through the train. The plug or gasket member also contains-a central opening 42 throughwhich the gases flow. The upper end of the tube 40 slides into a recess 46-the fitting 44 which is secured to the base.

or frame housing 71 of the apparatus by means of a i bracket '64. A plug member 50 is adapted'to slide within opening 52 is aligned with the opening 42 through the plug or gasket member 41. A tube 54 is welded to the outer end of the plug 5t} concentric with the opening 52.

qThe upper end of the tube extends through an opening 48in the bottom of the recess and connects with flexible tubing 56. A coil spring 53 or other resilient means is compressed between the plug and the bottom of the recess 46. Spring 58 urges the plug it) against the resilient surface of the plug 41. This provides a leaktight joint and provides a continuous passage from the inside of the tube to the flexible conduit 56 which connects the tube 4%) to the next element in the train.

A lever 6t extends from the plug 50 outwardly through a slot 62 cut in the wall of the fitting 44. This facilitates moving the plug 50 and its associated tube 54 against the compressive force of the spring 58 when it is desired to mount the tube 40 in the fitting.

The lower end of the tube 40 is disposed within a fixed fitting 66 which is secured to the frame 71 of the apparatus by means of a bracket 72. The fitting 66 has a recess 68 therein and a central opening 70 which connects the interior of the recess to tube '74 which in turn leads to the adjoining element in the train. If desired a slot may be provided through the wall of the fitting to permit moving the tube laterally into the recess instead of lifting it over the'wall. The resilient gasket or plug member 41 seats in fluid leak-tight relation with the bottom of the recess in the manner already described with respect to the top of the tube. In mounting tube 41 the plug 5% is de pressed against the compressive force of the spring 58 by using the lifting handle 60 and locking it in the recess 63. The plug 50 depresses a sufiicient distance to permit inserting the lower end of the tube in the recess 68 with the upper end in recess 46. It will be appreciated that the fitting 44 may take other forms and it is not our intention to limit the invention to the particular construction shown in FIGURE 2. Likewise, the gasket member 4-1 may take other forms as, for instance, the shape of an ordinary rubber washer as shown in FIGURES 6 and 7. In FIG- URES 3 through 5 another modification in the configuration of the sealing gasket is illustrated. In this form a hollow plug 81 made from rubber or other resilient ma terial has a wedge-shaped opening which terminates in a slit 82 in the concave upper portion thereof. As shown in FIGURE 3, the slit is closed so that no gas may pass into the tube when there is no pressure or force exerted on the convex end of the plug. In FIGURE 4 the plug is shown in compressed condition which results when the tube is mounted between the fittings illustrated in FIG- URE 2. Under the compressive force of the plug 50 the slit 82 opens up as indicated at 82'. Simultaneously the annular region 83 is brought into sealing relation with the spring biased plug 50. Internal wedge-shaped fillets 84 on either side of the valve member minimize the likelihood of gas being trapped in pockets inside the plug.

in FIGURE 6 We have shown a modified tube construction in which gas fiow may be effected only in one direction. The tube 89 has a restricted neck 94 at both ends and a circumferential rib 90 disposed a short distance inwardly from the neck 94. The rib or flange 99 supports a spring 91 having convolutions of decreasing diameter. The top convolution of the spring supports a ball valve 92 which may be made from plastic, glass, or other suitable material. The spring is adapted to compress when the pressure on the ball reaches two to three pounds per square inch. This tube may carry caps similar to those shown in FIGURES 2 through 5, or an ordinary rubber or neoprene washer as indicated at 95 may be used to seal the end of the tube against the bottom of the recess in the cooperating fitting. When the Washer 95 is used the tube should be inserted in place with the gas flow extant so that the recess containing the spring on the entrance end of the tube will be swept clear of room air and moisture before the spring seal is released.

In FIGURE 7 we have shown a tube which has a ground joint at one end. A ground glass plug fits into 6 a cooperating, outwardly flaring mouth 98 in the tube. The end of the plug 97 may be sealed either by a washer 95 or by a rubber cap placed over the end. The ground joint may be waxed in conventional manner without danger of plugging the capillaries and it is not necessary to disturb or wipe the joint during weighing. In this construction minimum contact between the flowing gas and the rubber or neoprene washer is maintained.

It will be apparent from the tube and sealing const'ructions illustrated in FIGURES 2 through 7 that many advantages accrue: No wax is required on the sealing members; no liquid or silicone lubricant or coating need be applied on the seals; there are no loose par-ts which can fall off when the tube is removed for weighing; the tube requires no wiping before weighing; no material on the seals can block the capillaries; the tubes can be disconnected quickly and easily; and they may be handled with forceps to eliminate weighing errors resulting from finger prints on the tube. Many of the advantages of the foregoing construction are also available in horizontally disposed tubes.

A modified form of a fitting 104 is illustrated in FIG- URE 8. The fitting 104 connects to a support member by means of a bracket 114. The plug 105 is tapped at 118 to receive the threaded end of the shaft 116. A lever 103 with a cam surface 11%) is pivotally mounted on the upper end of shaft 116 to permit lifting the plug and securing it in elevated position against the force of spring 106. The opening 166 in plug 105 is L-shaped, and provides communication between the interior of tube 49 and conduit 102 which extends through opening 112 in the wall of the fitting. By turning the threaded shaft 116, the compression of spring 106 may be adjusted. The conduit 102 is sufiiciently flexible to accommodate the small amount of movement that occurs when tube 40 is mounted in the fittings. The lower fitting, not shown, may be like fitting 66 of FIGURE 2, except that the opening therethrough for connection to the adjacent conduit may be L-shaped to match opening 109 in fitting 104.

Other advantages and modifications will also occur to those skilled in the art. It is not our intention to limit our invention other than as necessitated by the scope of the appended claims.

We claim:

1. In an analytical combustion train comprising a plurality of tubes interconnected by conduits including a vertical absorption tube containing solid particulate material, said particulate material serving to remove spe cific constituents from gases flowing through the train, which tube must be removed from the train for weighing, means for detachably incorporating said absorption tube in said train between the ends of adjacent conduits comprising a fitting fixed to a stationary base member and having a recess therein for receiving one end of said tube, a bore extending through said fitting to the recess, a conduit connected to said fitting in communication with said bore, a gasket member interposed between said one end of said tube and the bottom of said recess, a second fitting mounted on said stationary base member for receiving the other end of said tube, said second fitting having a recess fitted with a slidable plug, resilient means for urging said plug toward said other end of said tube, a bore extending through said second fitting to said recess, a gasket member interposed between said other end and said plug, and a conduit connected to said second fitting in communication with said bore.

2. The combustion train of claim 1 in which said gasket means comprises a stopper made from resilient material disposed in the end of said tube and having a bore therethrough, the outer end of said stopper which is normally in contact with the bottom of the recess in said fittings being convex.

3. The combustion train of claim 2 in which said bore constitutes a slit which opens only when said stopper is in compression to distend said convex end inwardly.

4. The combustion train of claim 1 in which said tube fiuidflow therethrough in one direction only.

5, The, combustion train of claim 1 inwhich said tube is fitted with ground glass stoppers inserted in the ends thereof which stoppers seat against said gasket members, said stoppers having an orifice therethrough.

, 6. In an analytical combustion train comprising a plurality of tubes interconnected'by conduits including an absorption tube containing solid-particulate material,

said particulate material serving to remove specific constituents from gases fiowing through the train, which tubemust be removed from the train for weighing,

means for detachably incorporating said absorption tube in said train between the ends of said adjacent conduits comprising a fixed fitting having a recess therein for receiving one end of said tube, a gasket member interposed between the end of said'tube and the bottom of said recess, a bore extending. externally of the fitting from said recess, one end of said conduit being connected to said fitting in communication with said bore, a second fitting containing an axially slidable member for receiving the other end of said tube, a gasket member interposed between said other end and said slidable member, resilient means for urging said slidable member toward said other end, a conduit connected to said movable fitting, and antopening through .said second fitting to establish communication between said conduit and the interior of said tube.

I 7. In an analytical combustion train including a vertically-disposedabsorption tube containing solid particulate material forabsorbing a constituentv from gas flowing through 'said tube, means for permitting quick removal of said tube from the train t'ofa'cilitate weighing said tube comprising" a fixed fitting having a recess for, receiving one end of said tube, a second fittinghaving vertically movable means'for receiving the other'end of said tube, a gasket interposed between each end of said tube and'the fitting cooperating therewith, said vertically movable means being biased toward said tube to compress the tube between the gaslretsjagainst said fixed fitting, and ,a conduit connecting to each fitting and communicating with the interior of said tube.v

References Cited in the file of this patent v v UNITED STATES PATENTS Heath Nov. 1,

" OTHER REFERENCES 7 Modern Laboratory Appliances, Fisher Scientific Company, 1952, pages 448- 9 

1.IN AN ANALYTICAL COMBUSTION TRAIN COMPRISING A PLURALITY OF TUBES INTERCONNECTED BY CONDUITS INCLUDING A VERTICAL ABSORPTION TUBE CONTAINING SOLID PARTICULATE MATERIAL, SAID PARTICULATE MATERIAL SERVING TO REMOVE SPECIFIC CONSTITUENTS FROM GASES FLOWING THROUGH THE TRAIN, WHICH TUBE MUST BE REMOVED FROM THE TRAIN FOR WEIGHING, MEANS FOR DETACHABLY INCORPORATING SAID ABOSORPTION TUBE IN SAID TRAIN BETWEEN THE ENDS OF ADJACENT CONDUITS COMPRISING A FITTING FIXED TO A STATIONARY BASE MEMBER AND HAVING A RECESS THEREIN FOR RECEIVING ONE END OF SAID TUBE, A BORE EXTENDING THROUGH SAID FITTING TO THE RECESS, A CONDUIT CONNECTED TO SAID FITTING IN COMMUNICATION WITH SAID BORE, A GASKET MEMBER INTERPOSED BETWEEN SAID ONE END OF SAID TUBE AND THE BOTTOM OF SAID RECESS, A SECOND FITTING MOUNTED ON SAID STATIONARY BASE MEMBER FOR RECEIVING THE OTHER END OF SAID TUBE, SAID SECOND FITTING HAVING A RECESS FITTED WITH A SLIDABLE PLUG, RESILIENT MEANS FOR URGING SAID PLUG TOWARD SAID OTHER END OF SAID TUBE, A BORE EXTENDING THROUGH SAID SECOND FITTING TO SAID RECESS, A GASKET MEMBER INTERPOSED BETWEEN SAID OTHER END AND SAID PLUG, AND A CONDUIT CONNECTED TO SAID SECOND FITTING IN COMMUNICATION WITH SAID BORE. 